1. Field of the Invention
The present invention generally relates to the field of digital image processing and, in particular, to methods and systems for processing scalable video data.
2. Description of the Related Art
The amounts of raw digital information included in high-resolution video sequences are massive and tend to increase along with advances in performance of video cameras. In order to reduce the amount of video data that must be transmitted to or processed by an end user system, various digital processing methods are used to compress the video data. In addition, many video applications require that, within a single stream, the video data is available at various resolutions. Therefore, compression and de-compression of video sequences are frequently performed during transmission or processing of video information; however, each of such conversions may degrade, objectively or subjectively, quality of visual information contained in the processed video data.
One of methods of scalable video coding (SVC) is spatial scalability technique (SSTs) used in industry-adapted video compression and communication standards, for example, MPEG-4, H.264 extension, and other standards. Using the SST, raw video data is divided into a low-resolution base layer and one or more enhancement layers. The base layer provides a lower quality video signal, while the enhancement layers contain additional information that can enhance the image corresponding to the base layer. Each enhancement layer can be combined with the base layer to form a video signal providing quality of visualization adapted to the requirements of a particular application.
Utilization of the SSTs requires development of low-pass re-sampling digital filters facilitating multiple layer coding, or image compression, of the high-resolution video data. Generally, image compression is controlled using quantization parameters, which define compression ratios of sampled, or compressed, video sequences and, as such, quality of reconstructed (i.e., decompressed) images.
In one example illustrating a need in sampling rate conversions using the SST, raw video data is down-sampled to reduce its resolution and then the data is encoded to produce the base layer. The base layer is decoded and reconstructed video data is up-converted to produce prediction data for the enhancement layer. Then, the prediction data is subtracted from the raw video data to produce residual data that, in an enhancement encoder, is encoded to form an enhancement layer.
During sampling rate conversions using the SST, conventional compression algorithms use re-sampling filters having fixed length and coefficients without considering quantization parameters, which may lead to unsatisfactory results. For example, subjective quality of some images may be too low. Therefore, despite the considerable effort in the art devoted to development of efficient methods and apparatus for sampling video data, further improvements would be desirable.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures, except that suffixes may be added, when appropriate, to differentiate such elements. The images in the drawings are simplified for illustrative purposes and are not depicted to scale. It is contemplated that features or steps of one embodiment may be beneficially incorporated in other embodiments without further recitation.
The appended drawings illustrate exemplary embodiments of the invention and, as such, should not be considered as limiting the scope of the invention that may admit to other equally effective embodiments.